Field
The present specification generally relates to optical fibers and, more specifically, to methods for making optical fiber preforms with low-index trenches.
Technical Background
Optical fibers with low-index trenches surrounding the core of the optical fiber may have improved bending performance and/or larger effective areas relative to comparable optical fibers which are formed without a low-index trench. Accordingly, the improved optical and physical properties of such fibers make them desirable for use in a variety of applications.
However, the formation of the low-index trench around the core of the optical fiber adds additional steps to the process of making an optical fiber preform and, as a result, adds significant costs to the process of making an optical fiber. Specifically, the low-index trench is formed by depositing silica-based glass around the core portion of the optical fiber and doping the silica-based glass with a down-dopant which decreases the index of refraction of the silica-based glass relative to the core portion of the optical fiber. However, to prevent the contamination of adjacent portions of the preform with the down-dopant, the low-index trench is separately formed and consolidated directly on the core portion of the optical fiber after the core portion has been consolidated and prior to depositing the overclad portion of the fiber. Specifically, the core portion of the optical fiber preform is first formed and consolidated to solid glass. Thereafter, the low-index trench portion is deposited around the core portion and then doped and consolidated in a separate step to prevent the dopant from diffusing into the core portion and the overclad portion. Finally, the overclad is formed around the low-index trench layer and consolidated in yet another step.
Accordingly, a need exists for alternative methods of forming an optical fiber preform comprising a low-index trench region surrounding the core portion.